A plasma display panel (hereinafter, called PDP) has a front plate and a rear plate. The front plate includes a glass substrate, display electrodes formed on a main surface of the glass substrate, a dielectric layer covering the display electrodes to function as a capacitor, and a protective layer made of magnesium oxide (MgO) formed on the dielectric layer. Meanwhile, the rear plate includes a glass substrate, data electrodes formed on a main surface of the glass substrate, a base dielectric layer covering the data electrodes, barrier ribs formed on the base dielectric layer, and phosphor layers respectively formed between the barrier ribs to emit red, green, and blue light.
The front plate and the rear plate are air-tightly sealed to each other with their electrode-formed surfaces facing each other. A discharge gas containing neon (Ne) and xenon (Xe) is enclosed in a discharge space divided by the barrier ribs. The discharge gas is electrically discharged to generate light when a video signal voltage is selectively applied to the display electrodes. The electric discharge generates ultraviolet light, and the generated ultraviolet light excites the phosphor layers. The excited phosphor layers respectively emit the red, green, and blue light. This is the mechanism of a color image display in PDP (see Patent Document 1).
There are four main functions exerted by the protective layer; 1) protect the dielectric layer from the impact of ions through the electric discharge, 2) release primary electrons to cause data discharge, 3) retain charges for causing the electric discharge, and 4) release secondary electrons during sustain discharge. Because the dielectric layer is protected from the ion-induced impact, a discharge voltage is prevented from increasing. As more primary electrons are released, a data discharge error, which is a factor responsible for flickering images, is reduced. Improvement of a charge retainability lowers a voltage to be applied, and increase of secondary electrons to be released lowers a sustain discharge voltage. An attempt for increasing the primary electrons to be released is to add, for example, silicon (Si) or aluminum (Al) to MgO of the protective layer (for example, see Patent Documents 1, 2, 3, 4, and 5).